2007i Hydra-Matic 6L90 (MYD)
Hydra-Matic 6L90 six-speed Car and Truck automatic transmission
2007i Model Year Summary
• New applications: Chevrolet Silverado 2500 HD, GMC Sierra 2500 HD
• Increased Torque Capacity
FULL DESCRIPTIONS OF NEW OR CHANGED FEATURES
NEW APPLICATIONS: CHEVROLET SILVERADO 2500 HD, GMC SIERRA 2500 HD
The Hydra-Matic 6L90 six-speed automatic transmission is available in the new GMT 900 series heavy-duty pickups, the Chevrolet Silverado 2500 HD and the GMC Sierra 2500 HD. Both applications use the 6.0L V8 engine.
INCREASED TORQUE CAPACITY
The Hydra-Matic 6L90 allows higher-torque output engines to be used in applications that do not require a heavy-duty, commercial-style transmission.
Overview
The Hydra-Matic 6L90 is six-speed automatic transmission for rear- and four-wheel-drive trucks, designed with modular flexibility and compatibility with advanced electronic controls. It is a heavy-duty version of the 6L80 six-speed automatic, with a strengthened input gearset which has two additional pinion gears for six total, and a strengthened output gearset, that uses wider gears than the 6L80. The 6L90 shares about 75 percent of the parts as the 6L80, although the case of the 6L90 is 35mm longer than the 6L80 case.
The 6L90 has the capability for adaptive shift controls and other features such as grade braking, and Driver Shift Control with tap up/tap down shifting. A wide overall ratio spread of 6.04:1 allows a “steep” first gear, as well as very “tall” overdrive top gear for low-rpm highway cruising. With this wide ratio spread, acceleration is maximized, as is fuel economy. Engine noise is also lower during cruising. Both fifth and sixth gears are “overdrive” gears, for example.
As in the 6L80, gear changes from second to sixth gears are accomplished with clutch-to-clutch control, where an oncoming clutch is engaged and an “offgoing” clutch is released in a precise manner to achieve the ratio change. The first-to-second upshift, however, is a freewheeling action, where the second gear clutch engages while the first gear one-way clutch spins freely. This allows a greater degree of smoothness at lower vehicle speeds. The clutch-to-clutch shifting and single freewheeler allows significant reductions in packaging requirements.
Advances in transmission control modules allow the modules to exist reliably inside the transmission, where temperatures remain fairly constant compared to a body-mounted module. The transmission and module are assembled together, so no additional steps are necessary during vehicle assembly.
The 32-bit transmission control module (TCM) monitors transmission performance and compensates for normal wear in components such as clutch plates, so transmission performance remains consistent for the life of the transmission. The control module also “tests” the components of the transmission following assembly to optimize the interaction of the components. The module is compatible with future global applications.
DEXRON® VI premium fluid validated to improve durability and shift stability
A new transmission fluid, DEXRON® VI, was developed to have a more consistent viscosity profile; a more consistent shift performance in extreme conditions; and less degradation over time. Internal GM tests have demonstrated DEXRON® VI delivers more than twice the durability and stability in friction tests compared to existing fluids. The DEXRON® VI fluid was designed specifically and validated for the new family of GM six-speed automatic transmissions.
The 6L90 variant of the new Hydra-Matic six-speed automatics centers on the desire for common components and manufacturing tooling. The 6L90 six-speed contains three gearsets, a conventional input planetary gearset with four pinion gears, as well as one compound output gearset and one simple output gearset. The compound output gearset uses three sets of pinion gear pairs, with one set of pinions meshing with the sun gear and the other set with the ring gear. This arrangement allows for optimal ratio steps with a 6.04 overall ratio spread.
The torque converter is 300mm in diameter, and is available initially with a single-plate lockup clutch, which makes use of GM’s proprietary electronic controlled capacity clutch (ECCC) technology, which uses a small, regulated amount of slip to dampen out engine pulses. This creates a smoother running drivetrain, especially during shift events.
Low maintenance
For severe use, DEXRON® VI fluid changes are the only maintenance recommended. For normal use there is no fluid change scheduled.
The Hydra-Matic 6L90 is produced in Ypsilanti, Michigan.
